Hello Ecarodiaz,
Thanks for your post. We'll continue working together to find the answer. Next, we recommend these steps:
• Check the "Sidecar system requirements" in this link: Use your iPad as a second display for your Mac with Sidecar.
• Make sure that both your iPad and MacBook Air models appear on the list.
• Then confirm these "Additional requirements
Both devices must be signed in to iCloud with the same Apple ID using two-factor authentication.
To use Sidecar wirelessly, both devices must be within 10 meters (30 feet) of each other and have Bluetooth, Wi-Fi, and Handoff turned on.
Also make sure that the iPad is not sharing its cellular connection and the Mac is not sharing its Internet connection.
To use Sidecar over USB, make sure that your iPad is set to trust your Mac."
If you continue to encounter a snag when setting up Sidecar, then Contact Apple Support for further assistance.
All the best!